The present invention relates to improvements in apparatus for stacking sheets, and more particularly to improvements in apparatus for converting one or more series or streams of successive sheets into one or more series of stacks or piles wherein the sheets accurately overlap each other. Still more particularly, the invention relates to improvements in apparatus for converting at least one series or stream of partially overlapping or non-overlapping sheets into a succession of stacks or piles on a support which is movable between an upper level (for reception of the lowermost sheet of a stack) and a lower level (for reception of the uppermost sheet of a stack). Still more particularly, the invention relates to improvements in sheet stacking apparatus wherein one or more endless overhead conveyors constitute or form part of means for transporting successive sheets of at least one series or stream of sheets against an abutment which serves as a stop for the leaders of successive sheets. If the sheets of at least one series or stream of sheets are transported along a substantially horizontal path, the abutment or stop is normally provided with a surface which confronts the oncoming sheets of the at least one series or stream and is normal or substantially normal to the path, i.e., the surface of the abutment or stop is normally located in or at least close to a vertical plane.
Apparatus of the type to which the present invention pertains can be utilized with advantage to simultaneously accumulate two or more sets of successive stacks from two or more series or streams of overlapping or non-overlapping sheets which are obtained by converting a relatively wide web of flexible sheet material into two or more narrower strips and by subdividing each strip into a succession of partially overlapping sheets (i.e., into imbricated or scalloped streams of sheets) or into a succession of non-overlapping sheets (i.e., into one or more streams wherein the trailing end of a preceding sheet does not overlap or is not overlapped by the leader of the immediately following sheet).
The apparatus of the present invention can be utilized with advantage for the stacking of sheets which consist of paper, metallic foil, plastic foil, textile material of woven or nonwoven fabric and/or any other flexible sheet-like material which is or which can be subdivided or formed into panels of a particular size for the stacking of such panels on top of one another. The invention will be described in greater detail in connection with the stacking of paper sheets having identical sizes but it is to be understood that sheets of a material other than paper can be stacked in the same way or in a similar way.
It is well known to convert a relatively wide running web of paper into two or more narrower webs or strips which are advanced lengthwise (the same as the wide web) and are thereupon acted upon by one or more cross cutters so that each strip yields a succession of discrete sheets having a width corresponding to that of the respective strip and a selected length. The thus obtained sheets can be converted into streams of successive partially overlapping (imbricated or scalloped) sheets or into streams wherein the leader of each next-following sheet overlies or is overlapped by the trailing end of the immediately preceding sheet. The sheets or each stream are normally gathered into a succession of stacks each having a predetermined number of preferably accurately overlapping sheets so that the stacks can be readily draped into panels of paper or other wrapping material prior to transport into storage or prior to introduction into boxes, crates or other types of receptacles.
Problems arise when the sheets of a stream of successive partially overlapping or non-overlapping sheets are relatively thin and relatively wide and/or relatively long. Such relatively wide and/or relatively long sheets are often used for conversion into blanks of documents having a particular format. The relatively thin and relatively large (e.g., relatively wide and/or relatively long) sheets must be handled with great care in order to ensure that their leaders will accurately overlie each other and will not undergo deformation during and/or as a result of stoppage at the stacking station. Otherwise stated, the transporting means and the stop for the leaders of such sheets must be designed to avoid deformation of and/or other damage to successive sheets during the last stage of advancement to the stacking station. The transporting means (particularly the customary overhead conveyor or conveyors of such transporting means) and the stop must cooperate to prevent buckling of the leaders of successive sheets during stoppage at the stacking station, as well as to ensure that each of a short or long series of successive sheets which are to form a stack is located in a predetermined plane not only during the last stage of transport toward the stop but also within the growing or fully grown pile at the stacking station.